DACs are well known in the art of electronic circuitry. A DAC converts digital input data into an analog output signal. A typical field of application is the processing of audio. Audio data is processed in the digital domain, e.g., as a piece of music stored on a DVD or downloaded from the Internet, but the result needs to be translated to an analog signal in order for a human being to consume it.
A characteristic of a DAC that co-determines its performance is referred to as “linearity”. The linearity of a DAC represents the property that for each change in the digital input data the analog output shows a proportionate change.
A typical configuration of a DAC comprises multiple current sources that are selectively switched to an output under control of the digital input. The currents are added at the output, and the value of the summed currents is representative of the digital data at the input.
A current-mode DAC preferably generates a differential current output for producing a differential voltage. In an electrically noisy environment, the noise voltage is usually a component common to both outputs and gets cancelled by taking the difference between the outputs. However, the differential output voltage may contain a contribution that is not proportional to the differential currents. This contribution is commonly referred to as the “common-mode” signal. DACs are designed so as to keep this common-mode signal as small as possible.